Mitchell Johnson's success at the Waca may have had more to do with the easterly wind than technique. Photograph: Tom Shaw/Getty Images

Imagine a leg‑break bowler who cannot bowl a googly or top‑spinner. Or an off‑break bowler without a drifter. Then contemplate the lot of a left-arm pace bowler whose sole modus operandi is to fire the ball across the bows of the right‑handed batsman and hope he chases one and edges. Think in fact of Alan Mullally. There are few things batsmen like more than a predictable bowler who spins or swings it one way only.

For two years, since he destroyed South Africa in Durban, until he did the same to England at the Waca, that was the fortune of Mitchell Johnson. Fast of course when he got it right, but the more he tried to swing the ball into the right‑hander, the delivery that is fundamental to any left‑arm paceman of ambition, the more it seemed to want to do the opposite.

So batsmen were able to play him on the line. Anything on the stumps and bat could be put to ball while anything off target could be ignored secure in the knowledge that it was not going to boomerang back and make them look foolish. Then, last Friday, in one inspirational bowling spell, that whole perception changed. From here on in it may not actually matter if Johnson gets another ball from the straight, for the notion has been planted that he might, and the threat is often as potent as the deed.

Quite how Johnson manages to swing the ball at all is a mystery, probably as much to him as anyone. Certainly he does not conform to the normal physical laws of orthodox swing bowling, where the seam is upright and a loose wrist promotes backward rotation on the ball to maintain its stability, like a gyroscope. No teachers of swing would need to look further than the seam position maintained by Jimmy Anderson at his best.

But this is all delivered from a high arm action. Johnson's bowling arm is so low, a round‑arm slingshot, that the umpires will soon be required to wear hard hats. So low indeed that he cannot physically get his wrist into the upright position that can deliver a perfect seam. In fact it was perplexing to see the television super-slow motion, which showed the seam scrambling on the way down, which is to say revolving randomly. Unless very occasionally the seam actually scrambles itself into the correct position by chance, it is hard to understand how the ball then swerves.

Nor is it quite the same as the movement obtained by the Sri Lankan fast bowler Lasith Malinga, with whom Johnson is often compared. However, the difference is considerable, Johnson's bowling arm coming round between 10 and 11 on a clock face, while Malinga "The Slinger" would barely reach 10 o'clock. The swing Malinga gets is more akin to that which might be seen with a Frisbee, a skimming motion, where the rotation on the ball is almost in a horizontal plane: swerve rather than swing in other words.

Instead, leaving aside all the reports of remedial work done since he was dropped from the Adelaide Test (which seem to range from eulogising Troy Cooley's biomechanics to a 10‑minute session with Dennis Lillee) the strongest theory regarding Johnson's performance in Perth relates to nothing more than the wind. From the second day onwards, the wind blew consistently oven-hot from the east, a counterpoint to the prevailing Fremantle Doctor, the cooling south‑westerly sea breeze that comes up the Swan River virtually on a daily basis at some stage in the afternoon. This easterly, say those who know the Waca well, is the wind that promotes swing.

But an understanding of why it happened makes it no easier to play. In fact, it was the arbitrary nature of his spell that contributed to England's downfall, for alert batsmen can look for clues in the bowler, from the way he holds the ball, to spotting the shiny side. Quite clearly Johnson tried to bowl considerably more of the inswinging delivery but succeeded only in pushing the ball wide instead as it refused to change course. Leaving the ball in such circumstance becomes fraught, to which Paul Collingwood would testify, his decision to offer no stroke too far gone to be able to react sufficiently quickly when the ball ducked into his pads.

It will be a surprise if Johnson can repeat his trickery at the MCG. Fully enclosed grounds can create their own micro-climate, but as with the Gabba it is not renowned as a swinging ground but rather one that can seam while the ball is new, and perhaps reverse swings later. The danger for England's batsmen now, though, is that because of the potential, there will be a temptation to want to play deliveries that until now their gameplan has been to avoid. It is a mindset they will do well to avoid although one it will be hard to avoid.

As Andy Flower has said about Perth, although the destructive spell came when the Australians had had a chance to work on the ball, there were indications with the newish ball to England's pair of left‑handed openers that he was just shaping the ball a fraction away from them. Perhaps the biggest clue will come from Ben Hilfenhaus and Ryan Harris, both of whom can swing the new ball. If they fail to get any real movement then the chances are that Johnson will not either.

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